1. Technical Field
The invention relates to tractor-trailer frames and subframes, and in particular, to subframes for trailers such as van trailers. More specifically, the invention is directed to a movable subframe comprising a combination of main members, cross-members, and cross braces interconnected by structural nodes and secured with an adhesive, for effectively reacting lateral, longitudinal, vertical, and racking loads to thereby securely support one or more axle/suspension systems suspended therefrom while reducing the overall weight of the subframe.
2. Background Art
Movable subframes, typically referred to as slider boxes, slider subframes, slider undercarriages, or slider secondary frames, have been utilized on tractor-trailers or semi-trailers for many years. One or more axle/suspension systems usually are suspended from a single slider box. For purposes of clarity, hereinafter the present invention will be referred to as a slider box. It is understood that a slider box outfitted with usually two axle/suspension systems typically is referred to as a slider or slider tandem, and again, for purposes of clarity will hereinafter be referred to as a slider tandem. The slider tandem in turn is mounted on the underside of the trailer frame, and is movable longitudinally therealong to provide a means for variable load distribution and vehicular maneuverability. More specifically, the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as limit the maximum load that can be supported by individual axles. A trailer having a slider tandem gains an advantage with respect to laws governing maximum axle loads. More particularly, proper placement of the slider tandem varies individual axle loads or redistributes the trailer load so that it is within legal limits. Once properly positioned, the slider tandem is locked in place on the underside of the trailer by a retractable pin mechanism.
Conventional or prior art slider box designs were developed before the advent of air suspension systems for trailers. At that time, leaf spring suspension systems were the suspension of choice for van trailer frames and slider boxes. However, the leaf spring suspension system was unable to provide much load distribution for varying load situations.
Moreover, the subsequent development of air suspension systems provided load equalization among multiple axles for tractor-trailers, with or without the utilization of slider boxes, as well as improved ride quality for individual axles. Of course, the combination of a movable slider box and an air suspension system provided maximum versatility with respect to variable load distribution and load equalization in a trailer. Unfortunately, prior art slider boxes equipped with air suspensions add unwanted weight to the trailer, primarily because those slider boxes were originally built to support spring suspensions and adapting them to incorporate air suspensions required additional bracing and support.
Additionally, vehicles containing more than one non-steerable axle, including tractor-trailers, are subject to lateral or side loads. Lateral loads can act through the slider box in opposite directions, and the effect of such bending loads on the slider box can be significant. Moreover, a slider box is subjected to strong vertical and longitudinal loads. Thus, the loads to which the slider box is subjected must be controlled by the slider box design. Prior art slider box designs control vertical loads by utilizing rigid, and therefore heavy, main members and cross members typically made of steel. The cross members typically are spaced-apart and parallel to one another, and perpendicular to the longitudinally extending elongated main members. A pair of K-shaped cross members, as shown, described and claimed in U.S. Pat. No. 5,720,489 assigned to the same assignee, Hendrickson USA, L.L.C., as the instant invention, also have been utilized. Although the device described in the '489 patent performed its function, room for improvement still exists particularly with respect to maintaining or increasing the overall strength of the slider while decreasing its weight.
Thus, within the trucking industry, reducing the weight of carrier equipment without sacrificing durability directly improves productivity by increasing the available payload that can be transported by the vehicle. Slider boxes made of steel have contributed to the excessive weight problems that have plagued slider tandems in the past. Although certain prior art slider boxes formed of steel have exhibited weight and durability improvement over other prior art steel slider boxes, such as the slider box of the '489 patent, the trucking industry continually is striving for additional improvement in slider box design. Moreover, attempts to utilize materials that are lighter than steel to construct slider boxes, such as aluminum, have been largely unsuccessful and inefficient.
The present invention solves the problems of excessive weight and structural deficiencies subject to potentially damaging lateral, longitudinal, vertical, and racking loads on tractor-trailer slider boxes, by the combination of: i) forming the slider box of aluminum; and ii) adhesively bonding the cross members and cross braces to each other and to the main members and frame hangers via a plurality of structural nodes which function to: 1) interconnect the main components of the slider box; and 2) generally evenly distribute loads between the main components of the slider box. The adhesive bonding provides good impact resistance to and distributes the loads over a large joint thus generally avoiding concentrated loadings between components, the latter of which is undesirable. Moreover, the combination of greater load distribution and reduced concentrated loadings at the connections permit lighter materials, such as aluminum, to be used to efficiently construct the slider box, thereby reducing the overall weight of the slider box without loss of structural integrity, but rather with an improvement thereto in a cost-efficient manner. It is understood that while the preferred embodiment of the present invention is directed to movable subframes or slider boxes, the concepts of the present invention also can be effectively applied to non-movable subframes and primary frames of heavy-duty vehicles.